Communication control method, mobility management device, home base station, and base station

ABSTRACT

A communication control method applied to a mobile communication system, the mobile communication system including a home base station that forms a specific cell and a mobility management device that performs verification of a user terminal for access permission to the specific cell in a handover procedure of the user terminal to the specific cell, comprises a step A of transmitting, by the mobility management device, verification failure information indicating failure of the verification to the home base station when the verification is failed after the user terminal establishes a connection to the specific cell in the handover procedure and a step B of starting, by the home base station, a re-handover procedure of the user terminal to another cell from the specific cell while maintaining the connection in response to reception of the verification failure information from the mobility management device.

TECHNICAL FIELD

The present invention relates to a communication control method, amobility management device, a home base station, and a base station in amobile communication system.

BACKGROUND ART

In 3GPP (3rd Generation Partnership Project) which is a project aimingto standardize a mobile communication system, specifications of a homebase station, which is a small base station provided in a home or acompany, are discussed (see Non Patent Document 1).

A home base station forms a specific cell such as a CSG (ClosedSubscriber Group) cell or a hybrid cell. The CSG cell is a cellaccessible only by a user terminal (called a “CSG member”) having anaccess permission. The hybrid cell is accessible by other terminalsother than the CSG member, but the CSG member is advantageously treated.

In addition, it is noted that a “cell” is used as a term indicating aminimum unit of a radio communication area, and is also used as a termindicating a function of performing radio communication with a userterminal.

In a handover procedure of a user terminal to a specific cell, amobility management device included in a core network performsverification (access control) of the user terminal for access permissionto the specific cell.

PRIOR ART DOCUMENT Non-Patent Document

Non-Patent Document 1: 3GPP technology specifications “TS 36.300V11.0.0” December, 2011

SUMMARY OF THE INVENTION

Meanwhile, there is considered a case in which a user terminal iserroneously handed over to a specific cell for which the user terminalhas no access permission depending on situations.

However, according to current specifications, there is a problem thatsuch a special case is not considered.

Therefore, an object of the present invention is to provide acommunication control method, a mobility management device, a home basestation, and a base station, with which it is possible to appropriatelycope with a case in which a user terminal is erroneously handed over toa specific cell for which the user terminal has no access permission.

A communication control method of the present invention is acommunication control method applied to a mobile communication system,the mobile communication system including a home base station that formsa specific cell and a mobility management device that performsverification of a user terminal for access permission to the specificcell in a handover procedure of the user terminal to the specific cell,and the communication control method comprises a step A of transmitting,by the mobility management device, verification failure informationindicating failure of the verification to the home base station when theverification is failed after the user terminal establishes a connectionto the specific cell in the handover procedure and a step B of starting,by the home base station, a re-handover procedure of the user terminalto another cell from the specific cell while maintaining the connectionin response to reception of the verification failure information fromthe mobility management device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a mobile communication system.

FIG. 2 is a protocol stack diagram of a radio interface.

FIG. 3 is a configuration diagram of a radio frame.

FIG. 4 is a block diagram of UE.

FIG. 5 is a block diagram of eNB.

FIG. 6 is a block diagram of MME.

FIG. 7 is a block diagram of HeNB.

FIG. 8 is a block diagram of HeNB GW.

FIG. 9 is a sequence diagram of a case 1 in which handover to a CSG cellis erroneously succeeded.

FIG. 10 is a sequence diagram of a case 2 in which handover to a CSGcell is erroneously succeeded.

FIG. 11 is a sequence diagram of a case 3 in which handover to a CSGcell is erroneously succeeded.

FIG. 12 is a sequence diagram of an operation pattern 1 according to anembodiment.

FIG. 13 is a sequence diagram of an operation pattern 2 according to theembodiment.

FIG. 14 is a sequence diagram of an operation pattern 3 according to theembodiment.

FIG. 15 is a flowchart of a transfer determination process of ameasurement report.

FIG. 16 is a flowchart of an acquisition method determination process ofthe measurement report.

FIG. 17 is a flowchart of a target cell determination process.

DESCRIPTION OF THE EMBODIMENT Overview of Embodiment

A communication control method according to an embodiment is applied toa mobile communication system including a home base station configuredto form a specific cell and a mobility management device configured toperform verification of a user terminal for access permission to thespecific cell in a handover procedure of the user terminal to thespecific cell. The communication control method includes a step A oftransmitting, by the mobility management device, verification failureinformation indicating failure of the verification to the home basestation when the verification is failed after the user terminalestablishes a connection to the specific cell in the handover procedure,and a step B of starting, by the home base station, a re-handoverprocedure of the user terminal to another cell from the specific cellwhile maintaining the connection in response to the reception of theverification failure information from the mobility management device.

In this way, even when the user terminal establishes a connection to aspecific cell for which the user terminal has no access permission inthe handover procedure (that is, when handover is erroneouslysucceeded), the re-handover procedure of the user terminal to the othercell from the specific cell is started while maintaining the connection,so that it is possible to prevent communication interruption fromoccurring in the user terminal.

In the present embodiment, the step A may comprise a step A1 oftransmitting, by the mobility management device, a negative response fora path switch request to the home base station together with theverification failure information on the basis of the path switch requestfrom the home base station. In the step A, the mobility managementdevice may transmit the verification failure information together withthe negative response.

In the present embodiment, the communication control method further maycomprises a step C of transferring, by a base station forming a sourcecell in the handover procedure, measurement information to the home basestation, the measurement information being at least a part of ameasurement report from the user terminal, and a step D of determining,by the home base station, the other cell on the basis of the measurementinformation from the base station.

In the present embodiment, in the step C, the base station may transferthe measurement information to the home base station at a time of dataforwarding or a handover request in the handover procedure.

In the present embodiment, in the step C, the base station may transferthe measurement information to the home base station when the specificcell is in a closed access mode.

In the present embodiment, in the step C, the base station transfers themeasurement information to the home base station when the verificationis omitted in the handover procedure.

In the present embodiment, the communication control method maycomprises a step E of transmitting, by the home base station, a transferrequest of the measurement information to the base station, and in thestep C, the base station may transfer the measurement information to thehome base station in response to the transfer request.

In the present embodiment, the communication control method further maycomprises a step F of transmitting, by the home base station, atransmission request of a measurement report to the user terminal inresponse to the reception of the verification failure information fromthe mobility management device, and a step G of determining, by the homebase station, the other cell on the basis of the measurement report fromthe user terminal.

A mobility management device of the present invention is a mobilitymanagement device performing verification of a user terminal for accesspermission to a specific cell in a handover procedure of the userterminal to the specific cell in a mobile communication system includinga home base station that forms the specific cell. The mobilitymanagement device comprises transmission unit that transmitsverification failure information indicating failure of the verificationto the home base station together with a negative response for a pathswitch request from the home base station when the verification isfailed after the user terminal establishes a connection to the specificcell in the handover procedure, control unit that controls the userterminal to be detached in response to transmission of the negativeresponse, and reception unit that receives a withholding request ofdetach of the user terminal from the home base station, wherein thecontrol unit withholds the detach of the user terminal in response ofreception of the withholding request by the reception unit.

A home base station of the present invention is a home base stationforming a specific cell in a mobile communication system including amobility management device that performs verification of a user terminalfor access permission to the specific cell in a handover procedure ofthe user terminal to the specific cell. The home base station comprisesreception unit that receives verification failure information indicatingfailure of the verification from the mobility management device when theverification is failed after the user terminal establishes a connectionto the specific cell in the handover procedure, and control unit thatcontrols a re-handover procedure of the user terminal to another cellfrom the specific cell to be started while maintaining the connection inresponse to reception of the verification failure information from themobility management device.

Abase station of the present invention is a base station forming asource cell in a handover procedure in a mobile communication systemincluding a home base station that forms a specific cell and a mobilitymanagement device that performs verification of a user terminal foraccess permission to the specific cell in the handover procedure of theuser terminal to the specific cell. The base station comprises transferunit that transfers measurement information to the home base station ata time of the handover procedure or at a time of reception of a transferrequest from the home base station, the measurement information being atleast a part of a measurement report from the user terminal.

Embodiment

In the present embodiment, an example of a mobile communication systemconfigured on the basis of 3GPP standards (that is, LTE-Advanced) afterrelease 10 will be described.

Hereinafter, (1) Overview of mobile communication system, (2) Blockconfiguration, (3) Operation, and (4) Conclusion of embodiment will besequentially described. In all drawings for explaining the followingembodiment, the same or similar reference numerals are used to designatethe same or similar elements.

(1) Overview of Mobile Communication System

FIG. 1 is a configuration diagram of a mobile communication systemaccording to the present embodiment. As illustrated in FIG. 1, themobile communication system includes a user terminal (UE: UserEquipment) 100, a base station (eNB: evolved Node-B) 200, a mobilitymanagement device (MME: Mobility Management Entity) 300, a home basestation (HeNB: Home evolved Node-B) 400, and a gateway device (HeNB GW:Home evolved Node-B Gateway) 500.

Each of the eNB 200, the HeNB 400, and the HeNB GW 500 is a networkdevice included in a radio access network (E-UTRAN: Evolved-UMTSTerrestrial Radio Access Network) 10. The MME 300 is a network deviceincluded in a core network (EPC: Evolved Packet Core) 20.

The UE 100 is a mobile radio communication device carried by a user. TheUE 100 performs radio communication with a cell (called a “servingcell”), with which an RRC connection has been established, in an RRCconnected state corresponding to a state during communication.

When the UE 100 moves together with the movement of a user, a change inthe serving cell of the UE 100 is necessary. An operation, in which theUE 100 changes the serving cell in an RRC connected state, is called“handover”. A series of procedures of the handover are called a“handover procedure”. The handover procedure includes a handoverpreparation stage (H.O. Preparation), a handover execution stage (H.O.Execution), and a handover completion stage (H.O. Completion).

In the present embodiment, the UE 100 employing a cell of the eNB 200 asa serving cell moves toward a cell of the HeNB 400, thereby performinghandover from the cell of the eNB 200 to the cell of the HeNB 400. Inthis case, in the handover procedure, the cell of the eNB 200 is a“source cell” and the cell of the HeNB 400 is a “target cell”.

The eNB 200 is a macro base station (MeNB), a pico base station (PeNB),or a home base station (HeNB). In the present embodiment, a descriptionwill be provided for an example in which the eNB 200 is considered to beMeNB. The eNB 200 forms one cell or a plurality of cells. The eNB 200performs radio communication with the UE 100.

The eNB 200 has a determination right of handover for the UE 100subordinate to the cell of the eNB 200. Specifically, the eNB 200 isable to determine whether to perform handover of the UE 100 to the cellof the HeNB 400 on the basis of a measurement report (MeasurementReport) from the UE 100.

The eNB 200 communicates with the EPC 20 through an S1 interface that isa logical communication path between the eNB 200 and the EPC 20.Specifically, the eNB 200 communicates with the MME 300 through anS1-MME interface which is a kind of the S1 interface. Moreover, the eNB200 is able to perform inter-base station communication with an adjacentHeNB 400 through an X2 interface that is a logical communication pathbetween the adjacent HeNB 400 and the eNB 200.

The MME 300 is provided corresponding to a control plane dealing withcontrol information, and performs various types of mobility managementor verification processes for the UE 100. The MME 300 performs theverification (hereinafter, “CSG verification”) of the UE 100 for accesspermission to the CSG cell.

A general handover procedure to the CSG cell uses the S1 interface.Specifically, the MME 300 performs the CSG verification of the UE 100,specifically, confirms whether the UE 100 is a member of the CSG cell.When it is confirmed that the UE 100 is the member of the CSG cell (thatis, in the case of CSG verification success), the handover of the UE 100to the CSG cell is possible. On the other hand, when it is not confirmedthat the UE 100 is the member of the CSG cell (that is, in the case ofCSG verification failure), the handover of the UE 100 to the CSG cell isrejected.

The HeNB 400 is a small stationary radio communication deviceinstallable within the house. The eNB 200 forms a specific cell having acoverage narrower than that of a cell. The specific cell is called a“CSG cell (a closed mode)”, a “hybrid cell (a hybrid mode)”, or an “opencell (an open mode)” according to a set access mode.

The CSG cell is a cell accessible only by a UE 100 (called a “member”)having an access permission, and broadcasts CSG ID. The UE 100 holds alist (called a “white list”) of CSG ID for which the UE 100 has anaccess permission, and determines the presence or absence of accesspermission, on the basis of the white list, and the CSG ID broadcastedby the CSG cell.

The hybrid cell is a cell in which the member is more advantageouslytreated as compared with a non-member, and broadcasts information (CSGIndication), which indicates that the hybrid cell is a cell released tothe non-member, in addition to the CSG ID. The UE 100 determines thepresence or absence of access permission on the basis of the white list,and the CSG ID broadcasted by the hybrid cell.

As described above, the UE 100 confirms the presence or absence ofaccess permission on the basis of the white list, but the white listmanaged by the UE 100 and CSG subscriber information (CSG SubscriptionData) managed by the MME 300 are not always synchronized with eachother. Therefore, basically, in a handover procedure of the UE 100 tothe CSG cell or the hybrid cell, the CSG verification of the UE 100 bythe MME 300 is necessary.

The open cell is a cell in which the UE 100 is equivalently treatedregardless of whether the UE 100 is a member, and does not broadcast theCSG ID. In view of the UE 100, the open cell is equal to a normal cell.

Hereinafter, a description will be provided for the case in which a cell(a specific cell) of the HeNB 400 is considered to be the CSG cell.

The HeNB 400 communicates with the MME 300 via the HeNB GW 500 throughthe S1 interface (the S1-MME interface). However, when the S1 interfacenot via the HeNB GW 500 is established between the HeNB 400 and the MME300, the HeNB 400 is able to directly communicate with the MME 300,without undergoing the HeNB GW 500. The HeNB 400 is connected (an X2connection) to the eNB 200 through the X2 interface.

The HeNB GW 500 manages a set of a plurality of HeNBs 400 between theEPC 20 (the MME 300) and the plurality of HeNBs 400. In view of the MME300, the HeNB GW 500 is equal to the HeNB 400. On the other hand, inview of the HeNB 400, the HeNB GW 500 is equal to the MME 300. The HeNBGW 500 communicates with the MME 300 as a representative of theplurality of HeNBs 400, thereby reducing traffic to be transmittedto/received from the MME 300. Furthermore, the HeNB GW 500 is able torelay data from one HeNB 400 managed by the HeNB GW 500 to another HeNB400.

FIG. 2 illustrates a protocol stack of a radio interface of the mobilecommunication system (an LTE system) according to the presentembodiment.

As illustrated in FIG. 2, the radio interface protocol is classifiedinto a layer 1 to a layer 3 of an OSI reference model, wherein the layer1 is a physical (PHY) layer. The layer 2 includes a MAC (Medium AccessControl) layer, an RLC (Radio Link Control) layer, and a PDCP (PacketData Convergence Protocol) layer. The layer 3 includes an RRC (RadioResource Control) layer.

The PHY layer performs data coding/decoding, modulation/demodulation,antenna mapping/demapping, and resource mapping/demapping. The PHY layerprovides a transmission service to an upper layer using a physicalchannel. Between a PHY layer of the UE 100 and a PHY layer of eNB (theeNB 200 or the HeNB 400), data is transmitted through the physicalchannel. The PHY layer is connected to the MAC layer through a transportchannel.

The MAC layer performs preferential control of data, and aretransmission process and the like by hybrid ARQ (HARQ). Between a MAClayer of the UE 100 and a MAC layer of the eNB (the eNB 200 or the HeNB400), data is transmitted through the transport channel. The MAC layerof the eNB (the eNB 200 or the HeNB 400) includes MAC scheduler fordetermining a transport format and a resource block of an uplink and adownlink. The transport format includes a transport block size, amodulation/coding scheme (MCS), and antenna mapping.

The RLC layer transmits data to an RLC layer of a reception side usingthe functions of the MAC layer and the PHY layer. Between an RLC layerof the UE 100 and an RLC layer of the eNB (the eNB 200 or the HeNB 400),data is transmitted through a logical channel.

The PDCP layer performs header compression/extension andencryption/decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB (the eNB 200 or the HeNB400), data is transmitted through a radio bearer. The RRC layer controlsthe logical channel, the transport channel, and the physical channel inresponse to establishment, re-establishment, and release of the radiobearer. When there is an RRC connection between RRC of the UE 100 andRRC of the eNB (the eNB 200 or the HeNB 400), the UE 100 is in an “RRCconnected state”. Otherwise, the UE 100 is in an “RRC idle state”.

A NAS (Non-Access Stratum) layer positioned above the RRC layer isprovided in the UE 100 and the MME 300 to perform session management ormobility management.

FIG. 3 is a configuration diagram of a radio frame used in the mobilecommunication system (an LTE system) according to the presentembodiment. The LTE system employs OFDMA (Orthogonal Frequency DivisionMultiplexing Access) in a downlink and SC-FDMA (Single Carrier FrequencyDivision Multiple Access) in an uplink.

As illustrated in FIG. 3, the radio frame includes 10 subframes arrangedin a time-period direction, wherein each subframe includes two slotsarranged in the time-period direction. Each subframe has a length of 1ms and each slot has a length of 0.5 ms. Each subframe includes aplurality of resource blocks (RBs) in a frequency direction, and aplurality of symbols in the time-period direction. Each symbol isprovided at a head thereof with a guard interval called a cyclic prefix(CP).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the other interval of each subframe is adata region mainly used as a physical downlink shared channel (PDSCH).In the downlink, reference signals (RS) different from each other ineach cell are transmitted.

In the uplink, both end portions in the frequency direction of eachsubframe are control regions mainly used as a physical uplink controlchannel (PUCCH). Furthermore, the center portion in the frequencydirection of each subframe is a data region mainly used as a physicaluplink shared channel (PUSCH).

(2) Block Configuration

Hereinafter, the block configurations of the UE 100, the eNB 200, theMME 300, the HeNB 400, and the HeNB GW 500 will be described.

(2.1) UE

FIG. 4 is a block diagram of the UE 100. As illustrated in FIG. 4, theUE 100 includes a radio transmission/reception unit 110, a storage unit120, and a control unit 130.

The radio transmission/reception unit 110 transmits/receives a radiosignal.

The storage unit 120 stores various types of information that is usedfor the control by the control unit 130. The control unit 130 controlsvarious functions of the UE 100. In an RRC connected state, the controlunit 130 controls the radio transmission/reception unit 110 to performradio communication with a serving cell.

The storage unit 120 stores a white list. The white list is updated bythe control unit 130. In the RRC connected state, the control unit 130updates the white list in response to a white list update message fromthe MME 300. Alternatively, in an idle state, the control unit 130 mayupdate the white list in response to information which is manuallyinput.

Furthermore, the storage unit 120 stores location information(fingerprint information) on the location of a CSG cell for which the UE100 has an access permission.

When the UE 100 is in the RRC connected state in the cell of the eNB200, if it is detected that the UE 100 entered the vicinity of the CSGcell, for which the UE 100 has an access permission, on the basis of thelocation information (the fingerprint information) on the location ofthe CSG cell for which the UE 100 has an access permission, then thecontrol unit 130 controls the radio transmission/reception unit 110 totransmit proximity notification (Proximity Indication) to the eNB 200.

When the radio transmission/reception unit 110 receives measurementcontrol information (Measurement configuration) on the CSG cell from theeNB 200 in response to the proximity notification, the control unit 130controls the radio transmission/reception unit 110 to transmit ameasurement report including a physical identifier (PCI: Physical CellIdentifier) of the CSG cell to the eNB 200.

When the radio transmission/reception unit 110 receives requestinformation (SI request) requesting the acquisition of broadcastinformation (SI: System Information) from the eNB 200 in response to themeasurement report, the control unit 130 acquires broadcast informationof the CSG cell and controls the radio transmission/reception unit 110to transmit a measurement report based on the broadcast information tothe eNB 200. The measurement report includes an identifier (CGI: CellGlobal Identifier) of the CSG cell, a tracking area identifier (TAI),CSG ID, and status information (Membership status) indicating whetherthe UE 100 is a CSG member.

In addition, the radio transmission/reception unit 110 receivesreference signals (RS) for each of a plurality of cells (serving cellsand adjacent cells). The control unit 130 measures reference signalreceived power (RSRP) and/or reference signal received quality (RSRQ)for each of the plurality of cells. The measurement report includes themeasurement information (RSRP/RSRQ) measured by the control unit 130 foreach of the plurality of cells. Specifically, the measurementinformation is obtained by associating an identifier of a cell withRSRP/RSRQ measured for the cell.

When the radio transmission/reception unit 110 receives a handovercommand (H.O. Command) to the CSG cell from the eNB 200, the controlunit 130 disconnects the RRC connection to the cell (a source cell) ofthe eNB 200, and starts a process of establishing an RRC connection tothe CSG cell of the HeNB 400.

(2.2) eNB

FIG. 5 is a block diagram of the eNB 200. As illustrated in FIG. 5, theeNB 200 includes a radio transmission/reception unit 210, a networkcommunication unit 220, a storage unit 230, and a control unit 240.

The radio transmission/reception unit 210 transmits/receives a radiosignal. Furthermore, the radio transmission/reception unit 210 forms onecell or a plurality of cells.

The network communication unit 220 communicates with the MME 300 throughthe S1 interface. The network communication unit 220 performs inter-basestation communication with the HeNB 400 through the X2 interface.

The storage unit 230 stores various types of information that is usedfor the control by the control unit 240.

The control unit 240 controls various functions of the eNB 200.

When the radio transmission/reception unit 210 receives the proximitynotification (Proximity Indication) from the UE 100 subordinate to theeNB 200, the control unit 240 controls the radio transmission/receptionunit 210 to transmit measurement control information (MeasurementConfiguration) for instructing measurement for the CSG cell to the UE100.

When the radio transmission/reception unit 210 receives the measurementreport including the physical identifier (PCI: Physical Cell Identifier)of the CSG cell from the UE 100 in response to the measurement controlinformation (Measurement Configuration), the control unit 240 controlsthe radio transmission/reception unit 210 to transmit the requestinformation (SI request) requesting the acquisition of broadcastinformation (SI: System Information) of the CSG cell to the UE 100.

When the radio transmission/reception unit 210 receives the measurementreport based on the broadcast information of the CSG cell from the UE100 in response to the request information, the control unit 240determines whether to perform handover of the UE 100 to the CSG cell onthe basis of the measurement report.

When it is determined to perform the handover of the UE 100 to the CSGcell, the control unit 240 controls the network communication unit 220to transmit a handover request (H.O. Request) to the HeNB 400 throughthe X2 interface.

Then, when a positive response (H.O. Request Ack) for the handoverrequest is obtained from the HeNB 400, the control unit 240 controls theradio transmission/reception unit 210 to transmit a command of thehandover (H.O. Command) to the CSG cell to the UE 100.

After the command of the handover to the CSG cell is transmitted, thecontrol unit 240 controls the network communication unit 220 to transfer(data forwarding) non-transmitted data to the UE 100, which remains in abuffer area of the storage unit 230, to the HeNB 400 through the X2interface.

At the time of the data forwarding, the control unit 240 may transferthe measurement report from the UE 100 to the HeNB 400. At this time,the control unit 240 extracts and transfers partial measurementinformation included in the measurement report from the UE 100, therebyreducing a data transfer amount.

Hereinafter, the measurement report (the measurement information)transferred from the eNB 200 to the HeNB 400 will be referred to as a“transfer measurement report”. The transfer measurement report is usedwhen performing a re-handover procedure from the CSG cell in the HeNB400 to another cell. The control unit 240 determines whether to transmitthe transfer measurement report to the HeNB 400 depending on situations.Details of the determination will be described later.

The control unit 240 extracts the partial measurement informationincluded in the measurement report from the UE 100, for example, usingthe following method.

The control unit 240 extracts the measurement information includingcommunication quality (RSRP/RSRQ) having a value higher than a thresholdvalue. When a large number of the measurement information is included inthe measurement report, the control unit 240 may extract n (for example,three) pieces of measurement information in a descending order of thecommunication quality (RSRP/RSRQ). Furthermore, in order to increase ahandover success rate to a target cell in the re-handover procedure, itis preferable that the control unit 240 more preferentially extractsmeasurement information including an identifier of a macro cell thanmeasurement information including an identifier of the CSG cell.

Moreover, the control unit 240 may allow additional information, otherthan the measurement information, to be included in the transfermeasurement report. The additional information is information indicatinga reception time of the measurement report from the UE 100. Theinformation indicating the reception time of the measurement report isincluded in the transfer measurement report, so that the HeNB 400 isable to determine newness (that is, reliability) of the transfermeasurement report. Alternatively, the additional information isinformation indicating a movement speed of the UE 100. In addition, themovement speed of the UE 100 is acquirable from the UE 100 or the EPC20.

(2.3) MME

FIG. 6 is a block diagram of the MME 300. As illustrated in FIG. 6, theMME 300 includes a network communication unit 310, a storage unit 320,and a control unit 330.

The network communication unit 310 communicates with the eNB 200 and theHeNB GW 500 through the S1 interface.

The storage unit 320 stores various types of information that is usedfor the control by the control unit 330. The storage unit 320 stores CSGsubscriber information (CSG

Subscription Data) regarding the access permission of the UE 100. TheCSG subscriber information (CSG Subscription Data) is obtained byassociating the identifier of the UE 100 with CSG ID of each CSG cellfor which the UE 100 has an access permission.

The control unit 330 controls various functions of the MME 300.

When updating the CSG subscriber information, the control unit 330 maycontrol the network communication unit 310 to transmit, to the UE 100, awhite list update message for updating the white list of the UE 100.

In the handover procedure from the cell of the eNB 200 to the CSG cellof the HeNB 400, when the network communication unit 310 receives a pathswitch request from the HeNB 400, the control unit 330 performs the CSGverification of the UE 100 on the basis of CSG ID, a cell access mode,and the identifier of the UE 100, which are included in the path switchrequest, and the CSG subscriber information stored in the storage unit320.

In addition, the path switch request indicates a message for requestinga communication path between the MME 300 and the EPC 20 to be switchedfrom the eNB 200 to the HeNB 400.

When the CSG ID and the identifier of the UE 100, which are included ina CSG verification request, are associated with the CSG subscriberinformation, the control unit 330 determines CSG verification successand controls the network communication unit 310 to transmit a positiveresponse (Path Switch Request Ack) for the path switch request to theHeNB 400 through the S1 interface.

Meanwhile, when the CSG ID and the identifier of the UE 100, which areincluded in the CSG verification request, are not associated with theCSG subscriber information, the control unit 330 determines CSGverification failure and controls the network communication unit 310 totransmit a negative response (Path Switch Request Failure) for the pathswitch request to the HeNB 400 through the 51 interface. In this case,the control unit 330 allows CSG verification failure information (CSGQuery Nack) indicating failure of the CSG verification to be included inthe negative response.

In addition, current specifications define that the MME 300 transmitsthe Path Switch Request Failure and then detaches the UE 100. However,after transmitting the Path Switch Request Failure, the control unit 330withholds the detach of the UE 100, in response to the networkcommunication unit 310 receiving a withholding request of the detach ofthe UE 100 from the HeNB 400.

(2.4) HeNB

FIG. 7 is a block diagram of the HeNB 400. As illustrated in FIG. 7, theHeNB 400 includes a radio transmission/reception unit 410, a networkcommunication unit 420, a storage unit 430, and a control unit 440.

The radio transmission/reception unit 410 transmits/receives a radiosignal. In the present embodiment, the radio transmission/reception unit410 forms the CSG cell. The CSG cell (the radio transmission/receptionunit 410) transmits broadcast information through BCCH (BroadcastControl Channel). The broadcast information includes CGI, TAI, and CSGID.

The network communication unit 420 communicates with the MME 300 via theHeNB GW 500 through the S1 interface. The network communication unit 420performs inter-base station communication with the eNB 200 through theX2 interface.

The storage unit 430 stores various types of information that is usedfor the control by the control unit 440.

The control unit 440 controls various functions of the HeNB 400.

When the network communication unit 420 receives the handover request(H.O. Request) from the eNB 200, the control unit 440 determines whetherto permit the handover request. When determining to permit the handoverrequest, the control unit 440 controls the network communication unit420 to transmit a positive response (H.O. Request Ack) for the handoverrequest to the eNB 200 through the X2 interface. On the other hand, whendetermining to reject the handover request, the control unit 440controls the network communication unit 420 to transmit a negativeresponse (H.O. Request Nack) for the handover request to the eNB 200through the X2 interface.

After the positive response (H.O. Request Ack) is transmitted, when thenetwork communication unit 420 receives data transferred (forwarded)from the eNB 200 through the X2 interface, the control unit 440 controlsthe data to be stored in the storage unit 430. When the data includesthe transfer measurement report, the control unit 440 acquires thetransfer measurement report, and controls the acquired transfermeasurement report to be stored in the storage unit 430.

Furthermore, after the positive response (H.O. Request Ack) istransmitted, when access from the UE 100 is detected, the control unit440 controls the radio transmission/reception unit 410 to establish anRRC connection to the UE 100.

After the RRC connection to the UE 100 is established, the control unit440 controls the network communication unit 420 to transmit a pathswitch request to the MME 300 through the S1 interface.

When the network communication unit 420 receives a positive response(Path Switch Request Ack) for the path switch request from the MME 300,the control unit 440 transmits forwarding data stored in the storageunit 430 to the UE 100, and then controls the radiotransmission/reception unit 410 and the network communication unit 420to transfer user data which is transmitted/received between the EPC 20and the UE 100.

On the other hand, when the network communication unit 420 receives anegative response (Path Switch Request Failure) for the path switchrequest from the MME 300, the control unit 440 confirms whether CSGverification failure information (CSG Query Nack) is included in thenegative response. When the CSG verification failure information (CSGQuery Nack) is included in the negative response, the control unit 440starts the re-handover procedure of the UE 100 to another cell from theCSG cell.

Until a handover command to another cell (a target cell) in there-handover procedure is transmitted to the UE 100 after the CSGverification failure information (CSG Query Nack) is received, thecontrol unit 440 controls the radio transmission/reception unit 410 tomaintain the RRC connection to the UE 100.

In addition, since the current specifications define that the MME 300transmits the Path Switch Request Failure and then detaches the UE 100,it is necessary to withhold the MME 300 from performing the detach ofthe UE 100. Therefore, when the network communication unit 420 receivesthe Path Switch Request Failure including the CSG Query Nack, thecontrol unit 440 controls the network communication unit 420 to transmita withholding request of the detach of the UE 100 to the MME 300 throughthe S1 interface.

In the re-handover procedure, in order to determine the other cell (thetarget cell), a measurement report (measurement information) obtained bymeasurement in the UE 100 is necessary. A method for acquiring themeasurement report includes the following three patterns.

In an operation pattern 1, the control unit 440 determines the targetcell on the basis of the transfer measurement report (that is, theforwarded transfer measurement report) stored in the storage unit 430.

In an operation pattern 2, the control unit 440 controls the networkcommunication unit 420 to request the eNB 200 to transmit the transfermeasurement report, thereby acquiring the transfer measurement reportfrom the eNB 200.

In an operation pattern 3, the control unit 440 controls the radiotransmission/reception unit 410 to request the UE 100 to transmit themeasurement report, thereby acquiring the measurement report from the UE100.

The control unit 440 determines one of the operation patterns 1 to 3,which is to be applied depending on situations. Details of thedetermination will be described later.

When determining the other cell (the target cell), the control unit 440controls the network communication unit 420 to transmit a handoverrequest to eNB forming the other cell. When a positive response (H.O.Request Ack) is received from the eNB, the control unit 440 controls theradio transmission/reception unit 410 to transmit, to the UE 100, ahandover command to the other cell.

(2.5) HeNB GW

FIG. 8 is a block diagram of the HeNB GW 500. As illustrated in FIG. 8,the HeNB GW 500 includes a network communication unit 510, a storageunit 520, and a control unit 530.

The network communication unit 510 communicates with the MME 300 and theHeNB 400 through the S1 interface.

The storage unit 520 stores various types of information that is usedfor the control by the control unit 530. In the storage unit 520, theHeNB 400 managed by the HeNB GW 500 has been registered.

The control unit 530 controls various functions of the HeNB GW 500. Thecontrol unit 530 manages a set of a plurality of HeNBs 400. The controlunit 530 controls the network communication unit 510 to communicate withthe MME 300 as a representative of the plurality of HeNBs 400.

(3) Operation

Hereinafter, the operation of the mobile communication system will bedescribed.

(3.1) Case in which Handover to CSG Cell is Erroneously Succeeded

Before describing the operation patterns 1 to 3 according to the presentembodiment, a description will be provided for cases 1 to 3 in whichhandover to a CSG cell is erroneously succeeded, as comparison examples.

(3.1.1) Case 1

FIG. 9 is a sequence diagram of a case 1 in which handover to a CSG cellis erroneously succeeded. The present sequence shows an operation afterthe eNB 200 determines the handover of the UE 100 to the CSG cell of theHeNB 400.

As illustrated in FIG. 9, in step P1, the eNB 200 transmits a query (CSGQuery) regarding whether the UE 100 is a member of the CSG cell of theHeNB 400 to the MME 300 through the S1 interface.

In step P2, the MME 300 confirms that the UE 100 is the member of theCSG cell of the HeNB 400, and transmits the confirmed fact (CSG QueryAck) to the eNB 200 through the S1 interface.

Then, in step P3, the MME 300 updates CSG subscriber information (CSGSubscription Data). A description will be given on the assumption thatthe UE 100 has not been the member of the CSG cell of the HeNB 400through the update.

In step P4, in response to the reception of the fact (CSG Query Ack)that the UE 100 is the member of the CSG cell of the HeNB 400, the eNB200 transmits a handover request (H.O. Request) for requesting handoverof the UE 100 to the CSG cell of the HeNB 400 to the HeNB 400 throughthe X2 interface. The HeNB 400 determines whether to permit acceptanceof the UE 100 in response to the handover request from the eNB 200.Hereinafter, a description will be given on the assumption that theacceptance of the UE 100 is permitted.

In step P5, the HeNB 400 transmits a positive response (H.O. RequestAck) for the handover request from the eNB 200 to the eNB 200 throughthe X2 interface.

In step P6, the eNB 200 transmits a handover command (H.O. Command) tothe CSG cell of the HeNB 400 to the UE 100 in response to the positiveresponse (H.O. Request Ack) from the HeNB 400.

In step P7, the UE 100 disconnects an RRC connection to the eNB 200 inresponse to the handover command from the eNB 200, and starts a processfor establishing an RRC connection to the CSG cell of the HeNB 400.

In step P8, the eNB 200 transfers (forwards) non-transmitted data, whichis directed to the UE 100, to the HeNB 400 through the X2 interface.

In step P9, the UE 100 establishes the RRC connection to the CSG cell ofthe HeNB 400. Specifically, in step P9-1, the UE 100 establishessynchronization with the CSG cell of the HeNB 400 with a random accessprocedure. In step P9-2, the HeNB 400 notifies the UE 100 of a timingadvance (TA) for adjusting a transmission timing of the UE 100. In stepP9-3, the UE 100 notifies the HeNB 400 of the fact that the RRCconnection to the CSG cell of the HeNB 400 is completely established.

In step P10, the HeNB 400 transmits a path switch request to the MME 300through the S1 interface. The path switch request includes CSG ID and acell access mode.

In step P11, the MME 300 performs CSG verification of the UE 100 on thebasis of the path switch request from the HeNB 400. As described above,since the UE 100 has not been the member of the CSG cell of the HeNB 400in the step P3, the CSG verification is failed.

In step P12, the MME 300 transmits a negative response (Path SwitchRequest Failure) for the path switch request from the HeNB 400 to theHeNB 400 through the S1 interface. The negative response includes CSGverification failure information (CSG Query Nack).

In step P13, the HeNB 400 disconnects the RRC connection to the UE 100in response to the negative response (Path Switch Request Failure) fromthe MME 300. As a consequence, the UE 100 is transitioned to an idlestate and communication is stopped.

(3.1.2) Case 2

FIG. 10 is a sequence diagram of a case 2 in which handover to a CSGcell is erroneously succeeded.

As illustrated in FIG. 10, the case 2 is different from the case 1 inthat no query (CSG Query) is transmitted to the MME 30 before thehandover request. When the cell of the HeNB 400 is a hybrid cell (is ina hybrid mode), even though the handover of the UE 100 to the cell isperformed, communication can be continued. Therefore, in the case 2,first of all, handover is performed, and the CSG verification isperformed using the path switch request.

However, when the cell of the HeNB 400 is a CSG cell (is in a closedmode), if the CSG verification is failed, the RRC connection between theUE 100 and the HeNB 400 is disconnected and communication is stoppedsimilarly to the case 1.

(3.1.3) Case 3

FIG. 11 is a sequence diagram of a case 3 in which handover to a CSGcell is erroneously succeeded.

As illustrated in FIG. 11, the case 3 is different from the case 1 inthat the query (CSG Query) is basically transmitted to the MME 30 beforethe handover request, and the query (CSG Query) to the MME 300 isexceptionally omitted. For example, there is considered an operation inwhich the handover request is made without the CSG verification onlywhen the white list of the UE 100 is reliable.

However, when the CSG verification using the path switch request isfailed, the RRC connection between the UE 100 and the HeNB 400 isdisconnected and communication is stopped similarly to the cases 1 and2.

(3.2) Operation Pattern According to Embodiment

Next, the operation pattern 1 to the operation pattern 3 according tothe embodiment will be described.

The operation pattern 1 to the operation pattern 3 according to theembodiment are common in that in response to the reception of the CSGverification failure information (CSG Query Nack) from the MME 300, theHeNB 400 starts the re-handover procedure of the UE 100 to another cellfrom the CSG cell while maintaining the RRC connection to the UE 100.

However, the operation pattern 1 to the operation pattern 3 according tothe embodiment have different methods for acquiring a measurement reportfor determining a target cell in the re-handover procedure.

(3.2.1) Operation Pattern 1

FIG. 12 is a sequence diagram of the operation pattern 1 according tothe embodiment. The present sequence shows an operation after the eNB200 transmits a handover request to the HeNB 400 and the HeNB 400determines to permit the handover request. Furthermore, in an initialstate of the present sequence, it is assumed that synchronization shiftoccurs between the white list of the UE 100 and the CSG subscriberinformation of the MME 300 (step S1).

As illustrated in FIG. 12, in step S2, the HeNB 400 transmits a positiveresponse (H.O. Request Ack) for the handover request from the eNB 200 tothe eNB 200 through the X2 interface.

In step S3, the eNB 200 transmits a handover command (H.O. Command) tothe CSG cell of the HeNB 400 to the UE 100 in response to the positiveresponse (H.O. Request Ack) from the HeNB 400.

In step S4, the UE 100 disconnects an RRC connection to the eNB 200 inresponse to the handover command from the eNB 200, and starts a processfor establishing an RRC connection to the CSG cell of the HeNB 400.

In step S5, the eNB 200 determines whether to transfer a measurementreport from the UE 100 to the HeNB 400. Hereinafter, a description willbe given on the assumption that it is determined to transfer themeasurement report from the UE 100 to the HeNB 400. In addition, detailsof the determination process (the step S5) will be described later.

In step S6, the eNB 200 transfers (forwards) non-transmitted data, whichis directed to the UE 100, to the HeNB 400 through the X2 interface.Furthermore, at the time of the forwarding, the eNB 200 transmits ameasurement report (a transfer measurement report) to the HeNB 400through the X2 interface. In addition, the measurement report (thetransfer measurement report) includes a received signal state (RSRPand/or RSRQ) measured by the UE 100 for at least one cell, and anidentifier of the cell.

In step S7, the UE 100 establishes the RRC connection to the CSG cell ofthe HeNB 400.

In step S8, the HeNB 400 transmits a path switch request to the MME 300through the S1 interface. The path switch request includes CSG ID and acell access mode.

In step S9, the MME 300 performs CSG verification of the UE 100 on thebasis of the path switch request from the HeNB 400. Since it isdetermined that the UE 100 is not the member of the CSG cell of the HeNB400, the CSG verification is failed.

In step S10, the MME 300 transmits a negative response (Path SwitchRequest Failure) for the path switch request from the HeNB 400 to theHeNB 400 through the S1 interface. The negative response includes CSGverification failure information (CSG Query Nack).

In step S10-1, in response to the reception of the Path Switch RequestFailure including CSG Query Nack, the HeNB 400 transmits a withholdingrequest of the detach of the UE 100 to the MME 300 through the S1interface. The MME 300 withholds the detach of the UE 100 in response tothe reception of the withholding request.

In step S11, the HeNB 400 starts a handover procedure of the UE 100 toanother cell in response to the reception of the CSG verificationfailure information (CSG Query Nack) from the MME 300. The HeNB 400determines an acquisition method of the measurement report from the UE100. In addition, details of the determination process (the step S11)will be described later. Hereinafter, a description will be given on theassumption that the transfer measurement report obtained through theforwarding (the step S6) in the handover procedure is acquired.

In step S12, the HeNB 400 determines a target cell in a re-handoverprocedure on the basis of the transfer measurement report obtainedthrough the forwarding (the step S6). Hereinafter, a description will begiven on the assumption that a cell, other than the cell of the eNB 200,is determined as the target cell. In addition, details of thedetermination process (the step S12) will be described later.

In step S13, the HeNB 400 transmits a handover request to the targetcell (target eNB) determined in the step S12. Furthermore, in the stepS14, the HeNB 400 notifies the eNB 200 of resource release (UE contextrelease) for the UE 100. Then, a normal handover procedure (are-handover procedure) is performed.

(3.2.2) Operation Pattern 2

FIG. 13 is a sequence diagram of the operation pattern 2 according tothe embodiment. Mainly, the differences from the operation pattern 1will be described, below.

As illustrated in FIG. 13, the operation pattern 2 is different from theoperation pattern 1 in that no measurement report (no transfermeasurement report) is transmitted to the HeNB 400 in forwarding (stepS6).

Furthermore, the operation pattern 2 is different from the operationpattern 1 in that after the CSG verification failure information (CSGQuery Nack) is received from the MME 300 (step S10), the HeNB 400requests the eNB 200 to transmit the transfer measurement report throughthe X2 interface (step S101) before determining the target cell (stepS12). The eNB 200 transmits the transfer measurement report to the HeNB400 through the X2 interface in response to the request of the HeNB 400(step S102).

(3.2.3) Operation Pattern 3

FIG. 14 is a sequence diagram of the operation pattern 3 according tothe embodiment. Mainly, the differences from the operation patterns 1and 2 will be described, below.

As illustrated in FIG. 14, the operation pattern 3 is different from theoperation patterns 1 and 2 in that the HeNB 400 acquires the transfermeasurement report from the UE 100 rather than from the eNB 200.

Specifically, after the CSG verification failure information (CSG QueryNack) is received from the MME 300 (step S10), the HeNB 400 transmits atransmission request (Measurement Configuration) of a measurement reportto the UE 100 (step S201) before determining the target cell (step S12).The UE 100 transmits the measurement report to the HeNB 400 in responseto the request of the HeNB 400 (step S202).

(3.3) Process Flow According to Embodiment

Next, detailed examples of processes in the operation pattern 1 to theoperation pattern 3 according to the embodiment will be described.

(3.3.1) Transfer Determination Process Flow of Measurement Report

FIG. 15 is a flowchart illustrating a transfer determination process ofa measurement report, that is, a detailed process of the aforementionedstep S5 (refer to FIG. 12 to FIG. 14).

As illustrated in FIG. 15, in step S51, the eNB 200 receives a handoverresponse (H.O. Request Ack) from the HeNB 400.

In step S52, the eNB 200 confirms whether a target cell (a cell of theHeNB 400) has CSG ID on the basis of a measurement report (MeasurementReport) from the UE 100. When the target cell has no CSG ID (the stepS52; Yes), the eNB 200 determines not to transfer the measurement report(step S53).

When the target cell has the CSG ID (the step S52; No), the eNB 200confirms whether CSG Indication of the target cell is False on the basisof the measurement report (Measurement Report) from the UE 100 in stepS54. When the CSG Indication of the target cell is False (the step S54;Yes), the eNB 200 determines not to transfer the measurement report (thestep S53). In addition, a cell having the CSG ID and the CSG Indicationof False corresponds to a hybrid cell.

When the CSG Indication of the target cell is True (the step S54; No),that is, when the target cell is a CSG cell (is in a closed mode), theeNB 200 confirms whether verification success information (CSG QueryAck) has been obtained from the MME 300 in step S55. When theverification success information has been obtained from the MME 300 (thestep S55; Yes), the eNB 200 determines not to transfer the measurementreport (the step S53).

When the verification success information has not been obtained from theMME 300 (the step S55; No), the eNB 200 confirms whetherpre-verification has been performed in step S56. The pre-verificationincludes verification using a white list, verification using CSGsubscriber information (CSG Subscription Data) copied from the MME 300,or a method for verifying the target cell in advance. When thepre-verification has been performed (the step S56; Yes), the eNB 200determines not to transfer the measurement report (the step S53).

When the pre-verification has not been performed (the step S56; No), theeNB 200 confirms whether a movement speed of the UE 100 exceeds athreshold value in step S57. When the movement speed of the UE 100exceeds the threshold value (the step S57; Yes), the eNB 200 determinesnot to transfer the measurement report (the step S53).

When the movement speed of the UE 100 is equal to less than thethreshold value (the step S57; No), the eNB 200 determines to transferthe measurement report (step S58).

In addition, in relation to the determination steps of the step S52, thestep S54, the step S55, the step S56, and the step S57 in the presentflow, as well as the case in which all the steps are performed, only apart of the steps may be performed.

(3.3.2) Acquisition Method Determination Process Flow of MeasurementReport

FIG. 16 is a flowchart illustrating an acquisition method determinationprocess of a measurement report, that is, a detailed process of theaforementioned step S11 (refer to FIG. 12 to FIG. 14).

As illustrated in FIG. 16, in step S111, the HeNB 400 receivesverification failure information (CSG Query Nack) from the MME 300.

In step S112, the HeNB 400 confirms whether a transfer measurementreport has been received from the eNB 200. When the transfer measurementreport has been received from the eNB 200 (the step S112; Yes), the HeNB400 determines to use the received transfer measurement report (stepS113).

When the transfer measurement report has not been received from the eNB200 (the step S112; No), the HeNB 400 confirms whether a movement speedof the UE 100 exceeds a threshold value in step S114. When the movementspeed of the UE 100 exceeds the threshold value (the step S114; Yes),the eNB 200 determines to request the eNB 200 to transfer themeasurement report (step S115).

When the movement speed of the UE 100 is equal to less than thethreshold value (step S114; No), the eNB 200 determines to request theUE 100 to transmit the measurement report (step S116).

In addition to the determination (the step S114) based on the movementspeed, in consideration of QoS of communication with the UE 100, whenthe QoS is high, it may be possible to determine to request the UE 100to transmit the measurement report. Furthermore, in consideration of anelapsed time period of the transfer measurement report, when the elapsedtime period is long, it may be possible to determine to request the UE100 to transmit the measurement report.

(3.3.3) Determination Process Flow of Target Cell

FIG. 17 is a flowchart illustrating a determination process of a targetcell, that is, a detailed process of the aforementioned step S12 (referto FIG. 12 to FIG. 14). In addition, in the operation pattern 3, sinceit is possible to determine the target cell using a normal method, thedetermination process of the target cell in the operation patterns 1 and2 will be described below.

In step S121, the HeNB 400 selects a cell (eNB) corresponding tomeasurement information with the second highest communication quality(RSRP/RSRQ) from measurement information included in the transfermeasurement report. In the transfer measurement report, since a cell ofthe HeNB 400 is considered to have the highest communication quality(RSRP/RSRQ), it is set as “the second highest”.

In step S122, the HeNB 400 confirms whether the cell selected in thestep S121 has the CSG ID. When the cell selected in the step S121 has noCSG ID (the step S122; Yes), the HeNB 400 selects the cell as the targetcell (step S123).

When the cell selected in the step S121 has the CSG ID (the step S122;No), the HeNB 400 confirms whether CSG Indication of the cell is Falseon the basis of the transfer measurement report in step S124. When theCSG Indication of the cell is False (the step S124; Yes), the HeNB 400selects the cell as the target cell (the step S123). In addition, a cellhaving the CSG ID and the CSG Indication of False corresponds to ahybrid cell.

When the CSG Indication of the cell is True (the step S124; No), thatis, when the cell is a CSG cell (is in a closed mode), in step S125, theHeNB 400 extracts measurement information corresponding to a cell havingno CSG ID from among the measurement information items with third andlower highest communication qualities (RSRP/RSRQ), included in thetransfer measurement report, and designates the highest communicationquality (RSRP/RSRQ) from thereamong. Then, the HeNB 400 confirms whetherthe difference between the second highest communication quality(RSRP/RSRQ) and the designated communication quality (RSRP/RSRQ) exceedsa threshold value.

When the difference exceeds the threshold value, the HeNB 400 selectsthe cell (the cell corresponding to the measurement information with thesecond highest communication quality (RSRP/RSRQ)), which is selected inthe step S121, as the target cell (the step S123).

On the other hand, when the difference is equal to or less than thethreshold value, the HeNB 400 selects a cell (that is, a cell used inthe comparison), which corresponds to the designated communicationquality (RSRP/RSRQ), as the target cell (step S126).

In addition to the present flow, the target cell may be determined asfollows. For example, since the eNB 200 (a source cell) holds settinginformation (context) of the UE 100, the source cell may bepreferentially selected as the target cell. Alternatively, a macro cellmay be preferentially selected as the target cell.

(4) Conclusion of Embodiment

As described above, after the UE 100 establishes an RRC connection tothe CSG cell in the handover procedure, when CSG verification is failed,the MME 300 transmits CSG verification failure information (CSG QueryNack) indicating the failure of the CSG verification to the HeNB 400.The HeNB 400 starts the re-handover procedure of the UE 100 to anothercell from the CSG cell while maintaining the RRC connection to the UE100 in response to the reception of the CSG verification failureinformation from the MME 300.

In this way, even when the UE 100 establishes the RRC connection to theCSG cell, for which the UE 100 has no access permission, in the handoverprocedure, the re-handover procedure of the UE 100 to another cell fromthe specific cell is started while maintaining the RRC connection, sothat it is possible to prevent communication interruption from occurringin the UE 100.

In the operation patterns 1 and 2 according to the embodiment, the eNB200 transfers at least a part of the measurement report of the UE 100 tothe HeNB 400. The HeNB 400 determines the target cell in the re-handoverprocedure on the basis of the transfer measurement report from the eNB200.

In this way, it is possible to quickly determine the target cell in there-handover procedure.

In the operation pattern 3 according to the embodiment, the HeNB 400determines the target cell in the re-handover procedure on the basis ofthe measurement report from the UE 100.

As described above, when the reliability of the transfer measurementreport is low (when the UE 100 moves at a high speed or when an elapsedtime period of the transfer measurement report is long), the measurementreport from the UE 100 is used instead of the transfer measurementreport, so that it is possible to appropriately determine the targetcell.

Other Embodiments

Thus, the present invention has been described with the embodiment andmodified examples. However, it should not be understood that thosedescriptions and drawings constituting a part of the present disclosurelimit the present invention.

For example, the aforementioned operation patterns 1 to 3 may beperformed through a combination thereof.

In the aforementioned operation pattern 1, the example, in which themeasurement report is transferred from the eNB 200 to the HeNB 400 atthe time of data forwarding in the handover procedure, is described.However, as well as at the time of the data forwarding, the measurementreport may be transferred from the eNB 200 to the HeNB 400 at the timeof the handover request (H.O. Request).

In addition, the entire content of U.S. Provisional Application No.61/612,055 (filed on Mar. 16, 2012) is incorporated in the presentspecification by reference.

INDUSTRIAL APPLICABILITY

As described above, a communication control method, a mobilitymanagement device, a home base station, and a base station according tothe present invention can appropriately cope with a case in which a userterminal is erroneously handed over to a specific cell for which theuser terminal has no access permission.

1. A communication control method applied to a mobile communicationsystem, the mobile communication system including: a home base stationthat forms a specific cell; and a mobility management device thatperforms verification of a user terminal for access permission to thespecific cell in a handover procedure of the user terminal to thespecific cell, the communication control method comprising: a step A oftransmitting, by the mobility management device, verification failureinformation indicating failure of the verification to the home basestation when the verification is failed after the user terminalestablishes a connection to the specific cell in the handover procedure;and a step B of starting, by the home base station, a re-handoverprocedure of the user terminal to another cell from the specific cellwhile maintaining the connection in response to reception of theverification failure information from the mobility management device. 2.The communication control method according to claim 1, wherein the stepA comprises a step A1 of transmitting, by the mobility managementdevice, a negative response for a path switch request to the home basestation together with the verification failure information on the basisof the path switch request from the home base station, the mobilitymanagement device is configured to detach the user terminal in responseto transmission of the negative response, and the step B comprises astep B1 of requesting, by the home base station, the mobility managementdevice to withhold detach of the user terminal.
 3. The communicationcontrol method according to claim 1, further comprising: a step C oftransferring, by a base station forming a source cell in the handoverprocedure, measurement information to the home base station, themeasurement information being at least a part of a measurement reportfrom the user terminal; and a step D of determining, by the home basestation, the other cell on the basis of the measurement information fromthe base station.
 4. The communication control method according to claim3, wherein in the step C, the base station transfers the measurementinformation to the home base station at a time of data forwarding or ahandover request in the handover procedure.
 5. The communication controlmethod according to claim 3, wherein in the step C, the base stationtransfers the measurement information to the home base station when thespecific cell is in a closed access mode.
 6. The communication controlmethod according to claim 3, wherein in the step C, the base stationtransfers the measurement information to the home base station when theverification is omitted in the handover procedure.
 7. The communicationcontrol method according to claim 3, comprising: a step E oftransmitting, by the home base station, a transfer request of themeasurement information to the base station, wherein in the step C, thebase station transfers the measurement information to the home basestation in response to the transfer request.
 8. The communicationcontrol method according to claim 1, further comprising: a step F oftransmitting, by the home base station, a transmission request of ameasurement report to the user terminal in response to the reception ofthe verification failure information from the mobility managementdevice; and a step G of determining, by the home base station, the othercell on the basis of the measurement report from the user terminal.
 9. Amobility management device that performs verification of a user terminalfor access permission to a specific cell in a handover procedure of theuser terminal to the specific cell in a mobile communication systemincluding a home base station that forms the specific cell, the mobilitymanagement device comprising: transmission unit that transmitsverification failure information indicating failure of the verificationto the home base station together with a negative response for a pathswitch request from the home base station when the verification isfailed after the user terminal establishes a connection to the specificcell in the handover procedure; control unit that controls the userterminal to be detached in response to transmission of the negativeresponse; and reception unit that receives a withholding request ofdetach of the user terminal from the home base station, wherein thecontrol unit withholds the detach of the user terminal in response ofreception of the withholding request by the reception unit.
 10. A homebase station that forms a specific cell in a mobile communication systemincluding a mobility management device that performs verification of auser terminal for access permission to the specific cell in a handoverprocedure of the user terminal to the specific cell, the home basestation comprising: reception unit that receives verification failureinformation indicating failure of the verification from the mobilitymanagement device when the verification is failed after the userterminal establishes a connection to the specific cell in the handoverprocedure; and control unit that controls a re-handover procedure of theuser terminal to another cell from the specific cell to be started whilemaintaining the connection in response to reception of the verificationfailure information from the mobility management device.
 11. A basestation which forms a source cell in a handover procedure in a mobilecommunication system including a home base station that forms a specificcell and a mobility management device that performs verification of auser terminal for access permission to the specific cell in the handoverprocedure of the user terminal to the specific cell, the base stationcomprising: transfer unit that transfers measurement information to thehome base station at a time of the handover procedure or at a time ofreception of a transfer request from the home base station, themeasurement information being at least a part of a measurement reportfrom the user terminal.